Pursuant to 35 U.S.C. xc2xa7119 and the Paris Convention Treaty, this application claims the benefit of Japanese Patent Application No. 2003-159188, filed on Jun. 4, 2003, and incorporated herein by reference.
1. Field of the Invention
This invention relates to evaporative fuel control system of an internal combustion engine, and more particularly to an evaporative fuel control system designed to avoid degradation in exhaust gas purification performance during the detection of possible evaporative fuel control system failure.
2. Description of Related Art
Traditional designs of internal combustion engines permit for unwanted air pollution and loss of fuel due to evaporation of fuel from the tank, the carburetor, and other engine components. To obviate these problems, modern automotive vehicles typically include evaporative fuel controllers (also known as evaporative fuel control systems, evaporative emission control systems, or simply EECSs), which generally employ fuel vapor collection canisters containing an adsorbent material, such as activated carbon, for adsorbing evaporative fuel, and a purge system for releasing the adsorbed fuel and supplying it to the engine at certain times conducive to such purging.
Because EECSs rely on pressure variations to desorb the evaporative fuel adsorbed by activated carbon and to forward it to the combustion chamber of the engine, if a failure of EECS occurs, e.g., when the EECS is compromised due to a physical damage, such as a crack or hole, or due to detachment of the fuel tank cap, evaporated fuel may be emitted into the ambient atmosphere in amounts greater than if these systems were not at all present in automotive vehicles. Thus, is important to provide for a built-in detection system and methods designed to diagnose evaporative fuel control system failure whenever EECSs are used.
Evaporative fuel control system failure detection devices have been described in the literature, for example, by Tadahiro (JP Laid-Open No. H11-343925) and Shingo, et al., (JP Laid-Open No. 2000-282972). Moreover, methods for diagnosing failure of evaporative purge systems (EPSs) utilizing negative pressure in the intake pipe have been disclosed in Japanese Patents Nos. 3139095, 3139096, 3106645, and 3139188, which are owned by the assignee of this invention.
However, EECS failure detection devices described in the literature suffer from a variety of operating problems. Specifically, a change in physical conditions, such as movement of fuel in the fuel tank, temperature rise as a result of engine operation, and variations in atmospheric pressure, can affect the vapor pressure in the fuel tank and thereby degrade the precision of failure diagnosis. In addition, because EFCS failure detection devices are designed to stop checking for failure under these circumstances, if a failure coincides with the change of physical conditions failure is not timely detected resulting in prolonged air pollution and loss of fuel.
To detect a failure of EECSs, it is preferable to apply negative pressure to the system and to determine whether it holds. However, if negative pressure is applied to the evaporative fuel control system so as to check for failure under conditions wherein the EECSs are operating normally and while much evaporative fuel resides in the evaporative system, the fuel-air mixture that is drawn into the engine becomes undesirably rich thereby resulting in incomplete combustion, rough engine operation and poor emissions. Thus there is an urgent need for EECSs and methods capable of detecting their own failure, wherein the diagnosis of failure is suspended at times when much evaporative fuel resides in the EECS detection passage.
The invention described herein provides an evaporative fuel control system for an internal combustion engine which system comprises an intake passage and a canister in communication with a fuel tank. The canister includes more than one chamber with an adsorbent material, such as activated carbon, provided to absorb evaporative fuel. In this system, the canister is connected to the atmosphere via an open passage which is controlled by the atmosphere open/close valve situated in the atmosphere open passage. The canister is also connected to the intake passage via a purge passage. The purge passage is controlled via a purge valve situated in the purge passage. The evaporative fuel control system comprises further a purge concentration detector which detects the concentration of a purge taken into the engine and a controller which diagnoses leakage after a predetermined amount of time calculated according to the concentration of the purge detected by the purge concentration detector. The diagnosis of leakage is not performed when a high concentration of evaporative fuel resides in the passage utilized for leak diagnosis. Thus, this evaporative fuel control system and methods avoid the detrimental effect of leak detection on the exhaust gas purification performance.
In certain embodiments, this invention is directed to an evaporative fuel control system for an internal combustion engine comprising: an intake passage; a canister disposed in an evaporative fuel control passage in communication with a fuel tank to absorb the evaporative fuel; an open passage to the atmosphere to communicate said canister with the atmosphere; an atmosphere open/close valve disposed in said atmosphere open passage; a purge valve disposed between said intake passage and said canister; a detector of the concentration of purge which purge is taken into said engine; and a controller for performing a diagnosis of failure of the evaporative fuel control system after a predetermined purge time has elapsed, said purge time being set according to the concentration of the purge detected by said detector.
In certain preferred embodiments, the predetermined purge time is set to be longer the higher the concentration of the purge. In a class of these embodiments the predetermined purge time is calculated according to the formula Tpurge=m1*(Purge Concentration)+a, wherein m1 is a number between 0 and 50; and a is a number between xe2x88x92500 and 500. In a subclass of this class, m1 is a number between 0 and 0.5, a is a number between 0 and 10, for purge concentrations lower or equal to 33.3%; m1 is a number between 0.4 and 5 and a is a number between xe2x88x92100 and xe2x88x9250, for purge concentrations higher than 33.3% but lower or equal to 50.0%; m1 is a number between 4 and 15 and a is a number between xe2x88x92400 and xe2x88x92300, for purge concentrations higher than 50.0% but lower or equal to 66.6%; and m1 is a number between 0 and 0.5, and a is a number between 150 and 250, and particularly about 180, for purge concentrations higher than 66.6%,.
In certain other preferred embodiments, the controller performs the diagnosis of failure while the atmosphere open/close valve is closed and the purge valve has been opened for a predetermined diagnosis time T1.
In certain other preferred embodiments, the controller prevents updating of the purge concentration value while the failure diagnosis is performed.
In certain other preferred embodiments, the predetermined diagnosis time T1 is set based on a temperature of the fuel system and/or a value of the atmospheric pressure.
In certain other preferred embodiments, the controller is capable of diagnosing failure due to a large leak within the evaporative fuel control system, such as a large leak resultant from a detachment of a fuel tank cap.
In certain other preferred embodiments, the controller performs the diagnosis of failure of the evaporative fuel control system only when the detector detects the purge concentration which is lower than 10%.
In other aspects, the invention is directed to methods of diagnosing failure of the evaporative fuel control system by executing the following steps: (a) waiting for the predetermined purge timeTpurge to elapse; (b) measuring the inner tank pressure GPT1 while the purge valve is closed and the atmosphere open/close valve is open; (c) closing the atmosphere open/close valve; (d) opening the purge valve; (e) measuring the inner fuel tank pressure PT while the purge valve is open and the atmosphere open/close valve is closed; and (f) comparing said pressure measured in step (b) to said pressure measured in step (e). In certain preferred embodiments, the failure of the evaporative fuel control system is positively diagnosed when the difference between the pressure measured in step (a) and the pressure measured in step (d) is lower than a predetermined reference value GPTL at the time when a predetermined diagnosis time T1 has elapsed.